1. Field of the Invention
The present disclosure generally relates to self-cleaning and/or antimicrobial compositions. More particularly, the disclosure generally relates to systems and methods for the customizable formation of antimicrobial compositions. Further, the disclosure generally relates to systems and methods for preparation of films and coatings using the prepared antimicrobial compositions.
2. Description of the Relevant Art
Bacteria exist in a variety of locations—in water, soil, plants, animals, and humans. Bacteria may transfer from person to person, among animals and people, from animals to animals, and through water and the food chain. Most bacteria do little or no harm, and some are even useful to humans; however, others are capable of causing disease. The same bacteria may have different effects on different parts of the host body. For example, S. aureus on the skin may be generally harmless, but when they enter the bloodstream they may cause disease.
An antimicrobial may be generally defined as anything that may kill or inhibit the growth of microbes (e.g., high heat or radiation or a chemical). Microbes may be generally defined as a minute life form, a microorganism, especially a bacterium that causes disease. Antimicrobials may be grouped into three broad categories: antimicrobial drugs, antiseptics, and disinfectants. Antimicrobial drugs may be used in relatively low concentrations in or upon the bodies of organisms to prevent or treat specific bacterial diseases without harming the organism. Antimicrobial drugs are also used in agriculture to enhance the growth of food animals. Unlike antimicrobial drugs, antiseptics and disinfectants are usually nonspecific with respect to their targets, they kill or inhibit a variety of microbes. Antiseptics may be used topically in or on living tissue. Disinfectants may be used on objects or in water.
Antimicrobial resistance may be generally described as a feature of some bacteria that enables them to avoid the effects of antimicrobial agents. Bacteria may possess characteristics that allow them to survive a sudden change in climate, the effects of ultraviolet light from the sun, and/or the presence of an antimicrobial chemical in their environment. Some bacteria are naturally resistant. Other bacteria acquire resistance to antimicrobials to which they once were susceptible.
The development of resistance to an antimicrobial is complex. Susceptible bacteria may become resistant by acquiring resistance genes from other bacteria or through mutations in their own genetic material (DNA). Once acquired, the resistance characteristic is passed on to future generations and sometimes to other bacterial species.
Antimicrobials have been shown to promote antimicrobial resistance in at least three ways: through (1) encouraging the exchange of resistant genes between bacteria, (2) favoring the survival of the resistant bacteria in a mixed population of resistant and susceptible bacteria, and (3) making people and animals more vulnerable to resistant infection. Although the contribution of antimicrobials in promoting resistance has most often been documented for antimicrobial drugs, there are reports of disinfectant use contributing to resistance and concerns about the potential for antiseptics to promote resistance. For example, in the case of disinfectants, researchers have found that chlorinated river water contains more bacteria that are resistant to streptomycin than does non-chlorinated river water. Also, it has been shown that some kinds of Escherichia coli (E. coli) resist triclosan (an antiseptic used in a variety of products, including soaps and toothpaste). This raises the possibility that antiseptic use could contribute to the emergence of resistant bacteria.
While antimicrobials are a major factor in the development of resistance, many other factors are also involved, including, for example, the nature of the specific bacteria and antimicrobial involved, the way the antimicrobial is used, characteristics of the host, and environmental factors. The use of antimicrobials does not always lead to resistance.
The Staphylococcus aureus bacterium (S. aureus), one of the most common causes of infections worldwide, has long been considered treatable with antimicrobial drugs. Recently, however, a number of S. aureus infections were found that resisted most available antimicrobials, including vancomycin, the last line of treatment for these and some other infections. For example, several years ago in Japan, a four-month-old infant who had developed an S. aureus infection following surgery, died after a month of treatments with various antimicrobials, including vancomycin. About a year later, three elderly patients in the United States with multiple chronic conditions were infected with this type of S. aureus, now known as vancomycin intermediate-resistant Staphylococcus aureus (VISA). They were treated with numerous antimicrobials for an extended period of time and eventually died, but it is unclear what role VISA played in their deaths. More recently, a middle-aged cancer patient in Hong Kong was admitted to a hospital with a fever and died despite two weeks of treatment for VISA.
Antimicrobials are recognized as major contributors in the development of antimicrobial resistance. There are many kinds of antimicrobials, varying in how they are used and in the agencies that have jurisdiction over them. The EPA is in fact conducting a reexamination of all pesticides (and antimicrobials), which received regulatory approval before 1984. In addition, the World Health Organization (WHO) has also repositioned itself to deal with this issue.
The causes for antimicrobial resistance are believed to be multi-factoral. In the case of antibiotics, it has been well documented that resistance is mainly caused by continued over reliance on and imprudent use of these antimicrobial agents. Increasing evidence is being obtained suggesting that the same may be true for the emergence of biocide resistance. There is increasing concern about possible cross-resistance of antibiotics and biocides due to common resistance mechanisms. The consequence of continued exposure to antimicrobials is an increase of bacteria that are intrinsically resistant to antimicrobials or have acquired resistance mechanisms to these substances.
Bacterial resistance mechanisms have been mostly determined for antibiotics and include: 1) exclusion from the cell (e.g., by the outer membrane); 2) enzymatic inactivation; 3) target alterations; and 4) active efflux from the cell. Similar resistance mechanisms are also involved in biocide resistance. Although exclusion from the cell due to reduced outer membrane impermeability was thought to play a key role in the intrinsic resistance of several common bacteria (e.g., P. aeruginosa) to many antimicrobial compounds, this is now attributed to synergy between a low-permeability outer membrane and active efflux from the cell. Some bacteria promote acquired multi-drug resistance as a consequence of hyper expression of the efflux genes by mutational events. In addition to antibiotics, these pumps export biocides, dyes, detergents, metabolic inhibitors, organic solvents and molecules involved in bacterial cell-cell communication. A discussion of mechanisms of antimicrobial resistance may be found in Schweizer, H. P. “Efflux as a mechanism of resistance to antimicrobials in Pseudomonas aeruginosa and related bacteria: unanswered questions” Genet. Mol. Res., 2(1): 48-62 (Mar. 31, 2003), which is incorporated by reference as if fully set forth herein.
Concern about possible cross-resistance of antibiotics and biocides due to common resistance mechanisms may be further accentuated when the mechanism of several different antimicrobials are compared. For example, the antimicrobial effects of silver salts have been noticed since ancient times, and today, silver is used to control bacterial growth in a variety of applications, including dental work, catheters, and burn wounds. Added at high (i.e., millimolar) concentrations, Ag+ ions inhibit a number of enzymatic activities, reacting with electron donor groups, especially sulfhydryl groups. However, research in the past few years of the molecular mechanism of the bactericidal effect of much lower (e.g., micromolar) concentrations of Ag+ ions points toward a different mechanism.
The addition of low micromolar concentrations of Ag+ to inside-out membrane vesicles of V. cholerae induced a total collapse of both ΔpH and Δψ irrespective of the presence of Na+ ions. This effect of Ag+ was independent of the presence of the Na+-translocating NADH:ubiquinone oxidoreductase (NQR), known as a specific target for submicromolar Ag+, suggesting that the other Ag+-modified membrane proteins (or perhaps the Ag+-modified phospholipid bilayer itself) may cause the H+ leakage, thus explaining the broad spectrum of the antimicrobial activity of Ag+ ions. It is possible that the bactericidal action of these concentrations of Ag+ in V. cholerae is not mediated by a specific target but is due to the H+ leakage occurring through virtually any Ag+-modified membrane protein or perhaps through the Ag+-modified phospholipid bilayer itself. In the absence of Ag+ resistance determinants (encoding pumps capable of efficient expelling of the Ag+ ion), this would result in a complete deenergization of the membrane. Taking into account the well-documented importance of the transmembrane proton gradient in overall microbial metabolism, it seems inevitable that the protonophore-like effect of Ag+ described here should result in cell death. A discussion of the antimicrobial properties of silver may be found in Dibrov et al. “Chemiosmotic Mechanism of Antimicrobial Activity of Ag+ in Vibrio cholerae” ANTIMICROBIAL AGENTS AND CHEMOTHERAPY, August 2002, Vol. 46, No. 8, 2668-2670, which is incorporated by reference as if fully set forth herein.
The antimicrobial effects of titanium dioxide have been known for quite some time and it is used to control bacteria activity. When titanium dioxide (TiO2) is irradiated with near-UV light, this semiconductor exhibits strong bactericidal activity. Evidence has been presented that appears to show that the lipid peroxidation reaction is the underlying mechanism of death of Escherichia coli K-12 cells that are irradiated in the presence of the TiO2 photocatalyst. Using production of malondialdehyde (MDA) as an index to assess cell membrane damage by lipid peroxidation, it was observed that there was an exponential increase in the production of MDA, whose concentration reached 1.1 to 2.4 nmol·mg (dry weight) of cells−1 after 30 min of illumination, and that the kinetics of this process paralleled cell death. Under these conditions, concomitant losses of 77% to 93% of the cell respiratory activity were also detected, as measured by both oxygen uptake and reduction of 2,3,5-triphenyltetrazolium chloride from succinate as the electron donor. The occurrence of lipid peroxidation and the simultaneous losses of both membrane-dependent respiratory activity and cell viability depended strictly on the presence of both light and TiO2. It was theorized that TiO2 photocatalysis promoted peroxidation of the polyunsaturated phospholipid component of the lipid membrane initially and induced major disorder in the E. coli cell membrane. Subsequently, essential functions that rely on intact cell membrane architecture, such as respiratory activity, were lost, and cell death was inevitable. A discussion of the antimicrobial properties of titanium dioxide may be found in Maness, P. et al. “Bactericidal Activity of Photocatalytic TiO2 Reaction: toward an Understanding of Its Killing Mechanism” APPLIED AND ENVIRONMENTAL MICROBIOLOGY, September 1999, Vol. 65, No. 9, 4094-4098, which is incorporated by reference as if fully set forth herein.
Phenol and its derivatives exhibit several types of bactericidal action. At higher concentrations, the compounds penetrate and disrupt the cell wall and precipitate cell proteins. Generally, gram-positive bacteria are more sensitive than gram-negative bacteria, which in turn are more sensitive than mycobacteria. The initial reaction between a phenolic derivative and bacteria involves binding of the active phenol species to the cell surface. Once the active phenol species has bound to the exterior of the cell, it needs to penetrate to its target sites-either by passive diffusion (gram-positive) or by the hydrophobic lipid bilayer pathway (gram-negative). One of the initial events to occur at the cytoplasmic membrane is the inhibition of membrane bound enzymes. The next level in the damage to the cytoplasmic membrane is the loss in the membrane's ability to act as a permeability barrier. There is limited information regarding the action of phenolics against viruses. The molecular mechanisms probably do not differ from those that occur in bacteria. Phenols act at the germination stage of bacterial spore development; however, this effect is reversible-therefore the sporicidal activity of phenolic compounds is low. As with many disinfectants, the activity of phenols is highly formulation dependant and affected by factors such as temperature, concentration, pH and the presence of organic matter.
The mode of action of quaternary ammonium compounds has not yet been completely described in detail, but there are definitive explanations of the antimicrobial mode of action of cationic disinfectants.
One of the main considerations in examining the mode of action is the characterization of quaternary ammonium compounds as cationic surfactants. Cationic surfactants reduce the surface tension at interfaces, and is attracted to negatively charged surfaces, including microorganisms. Quaternary ammonium compounds denature the proteins of the bacterial or fungal cell, affect the metabolic reactions of the cell and allow vital substances to leak out of the cell, finally causing death.
Current definitions of the different generations of quaternary ammonium compounds include:                First generation quaternary ammonium compounds: Benzalkonium chlorides. First generation quaternary ammonium compounds have the lowest relative biocidal activity and are commonly used as preservatives.        Second generation quaternary ammonium compounds: Substituted benzalkonium chlorides (e.g., alkyl dimethyl benzyl ammonium chloride). The substitution of the aromatic ring hydrogens with chlorine, methyl and/or ethyl groups resulted in second generation quaternary ammonium compounds with high biocidal activity.        Third generation quaternary ammonium compounds: (e.g., contain an equal mixture of alkyl dimethyl benzyl ammonium chloride+alkyl dimethyl ethylbenzyl ammonium chloride). This mixture of two specific quaternary ammonium compounds resulted in a dual quaternary ammonium compound offering increased biocidal activity, stronger detergency, and increased safety to the user (relative lower toxicity).        Fourth generation quaternary ammonium compounds: Dialkylmethyl amines (e.g., didecyl dimethyl ammonium chloride or dioctyl dimethyl ammonium chloride). Fourth generation quaternary ammonium compounds are superior in germicidal performance, lower foaming, and have an increased tolerance to protein loads and hard water.        Fifth generation quaternary ammonium compounds: Mixtures of fourth generation quaternary ammonium compounds with second-generation quaternary ammonium compounds (e.g., didecyl dimethyl ammonium chloride+alkyl dimethyl benzyl ammonium chloride). Fifth generation quaternary ammonium compounds have excellent germicidal performance, they are active under more hostile conditions and are generally safer to use.        
It may not always be the case that a disinfectant with a fifth-generation quaternary ammonium compound is better than one with a third-generation quaternary ammonium compound. The non-germicide components of a disinfectant also have an impact on overall performance. Quaternary ammonium compounds are extremely sensitive to hard water, and usually require a chelant in the formula to obtain efficacy in these conditions.
Glutaraldehyde-protein interactions indicate an effect of the dialdehyde on the surface of bacterial cells. Many of the studies indicate a powerful binding of the aldehyde to the outer cell layers. Because of this reaction in the outer structures of the cell, there is an inhibitory effect on RNA, DNA, and protein synthesis as a result.
In reacting with bacterial spores, studies have shown that acid glutaraldehyde could interact at the spores' surface and remain there, whereas alkaline glutaraldehyde could penetrate the spore. Thus, the role of the activator: an alkalinizing agent in facilitating penetration and interaction of glutaraldehyde with components of the spore cortex or core. Inhibition of germination, spore swelling, mycelial growth, and sporulation in fungal species at varying concentrations has been demonstrated. The principal structural wall component of many molds and yeast is chitin, which resembles the peptidoglycan of bacteria and is thus a potentially reactive site for glutaraldehyde action. In viruses, the main targets for glutaraldehyde are nucleic acid, proteins, and envelope constituents. The established reactivity of glutaraldehyde with proteins suggests that the viral capsid or viral-specific enzymes are vulnerable to glutaraldehyde treatment.
Ortho-phthalaldehyde is a claimed alternative aldehyde that is currently under investigation. Unlike glutaraldehyde, ortho-phthalaldehyde is odorless, stable, and effective over a wide pH range. It has been proposed that, because of the lack of alpha-hydrogens, ortho-phthalaldehyde remains in its active form at alkaline pH.
EDTA and other chelating agents are often added to the germicide formula to aid in activity in hard water conditions. These ingredients also add to the antimicrobial activity by chelating magnesium and calcium in the organism. EDTA has been shown to boost the effect of antimicrobial activity against gram-negative organisms such as Pseudomonas aeruginosa. 
Many antimicrobials function by attacking and disrupting the cell membrane causing the microbe to “bleed” to death. Other antimicrobials function by penetrating the cell membrane and subsequently inhibiting one or more functions within the cell. Therefore microbial adaptations, such as reduced outer membrane impermeability and active efflux from the cell, may reduce the effectiveness of many known and commonly used antimicrobials. Antimicrobial resistance has increased due to the over use and misuse of antimicrobials. Part of the problem has been attributed to antimicrobials which, due to their design, leach into the environment excessively overexposing microbes in the environment promoting antimicrobial resistance.
New antimicrobials are required to combat the new antimicrobial resistant microbes. New antimicrobials may be effective verses microbes which are currently resistant to currently known antimicrobials. New antimicrobials may resist leaching off into the environment beyond a predetermined amount to inhibit polluting the environment unnecessarily.